In image compositing, presence of noise, especially in the backing (screen) area, is an annoying problem. The presence of noise is more noticeable when full additive mix is applied, where a foreground image is processed by subtracting the screen components of the image, then added to a processed background image. This problem is made worse when foreground images are recorded on film. Film grain, especially in the blue layer, becomes visible noise.
When performing image compositing, eliminating or minimizing visual noise is a crucial factor for obtaining acceptable results. Most image compositing equipment use various techniques to eliminate noise, by amplifying and reshaping the matte or the key signal. Unfortunately, this results in loss of valuable fine detail from the foreground image, and gives an unnatural "cut and paste" look to the final composite. In many cases, this might be the only acceptable compromise.
Various filtering techniques (averaging, recursive) have been used to minimize visual noise. Unfortunately, simply filtering the whole picture makes the foreground subject look soft, with noticeable loss of fine detail. With recursive noise reduction techniques, moving or out of focus objects tend to lose part of the blurred edges, thus losing the natural look.